Selective switch



Dec- 29 1925.

Any

2 Sheets-Sheet 1 lm/enrq'rs: Fran/ 5W Reeves.

fdgar hf CYar/r.

F. N. REEVES ET AL SELECTIVE SWITCH Filed Dec. 29, 1919 A 5 3% 3h 2m 8% B ml 1,567,297 F. N. REEVES ET AL SELECTIVE SWITCH Dec- 29, 1925- Filed Dec. 29, 1919 2 Sheets-Sheet 2 /nVe/ 71ors- Frank N Ree ves.

fdgar H. C/ar/v.

Patented Dec. 29, 1925.

UNITED STATES PATENT orric's- EEAEK N. EEEvEs, 0E NEWARK, NEw .iEEsEY, AND EDGAR c'IlA K, or RICHMOND.

HILL, NEW YORK, ASSIGNORS T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK,

SELECTIVE swrrcir.

Application filed December 29, 1919. Serial No. 347,936.

To all whom it may concern:

Be it known that we, FRANK N. REnvEs and l lncnn H. CLARK, citizens of the United States, residing at Newark, in the countyof Essex, State of New Jersey, and Richmond Hill, in the county of Queens, State of: New York, respectively, have invented certain new and useful Improvements in Selective Switches, of which the following is full, clear, concise, and exact description.

This invention relates to selective switches and in particular to switches of the class used in extending connections in automatic telephone exchange systems.

Switches of this character comprise in general, a movable element consisting of brushes or contacts and a fined element consisting of a bank of stationary circuit terminals. The movable brushes are arranged to be criven, under the selective control of numerical controlling devices, into engagement with the stationary terminals of the bank. These stationary terminals are arranged in groups, the terminals of each of the several groups representing trunks or circuits leading to a group of succeeding switches of the same numerical order and the relative disposition of the groups in the bank depends on the kind of movement imparted to the brushes in their co-operation with said terminals. In certain types of selective switches the terminal groups are so arranged in the bank that the cooperating brushes by a continuous movement, either in a rectilinear or curvilinear direc' tion, may engage the terminals of successive groups. Since the terminals of each group usually represent trunks of a different numerical order from those of other groups, it is desirable to discontinue the movement of the brushes after they have hunted over any given group and found the same busy. To accomplish this, a set of terminals known as overflow terminals, is interposed between adjacent groups and serves to arrest the movement of the brushes at the end of each gr up to prevent said brushes from entering the following group.

it is the object of the present invention to provide switch of the foregoing character in which the movable element is arranged to be brought to rest on the engagement of A feature oit the invention relates to a switch in which the movable brushes, arranged to be arrested in engagement with the terminal sets of a group responsive to av given electrical condition of said terminals whereupon a circuit is completed to, the

movable brushes to alter said condition, are arrested when a particular set of terminals of said group is engaged without 'complet-. ing such circuit to aitect the electrical con dition of such particular terminals.

A more thorough understanding of the principles and advantages of this invention is to be had from a detailed description 01'' the switch in which the same is embodied.

in the drawings there is shown to the left of the vertical broken line in Fig. 1, a subscribers line terminating at an operators position in a manual office. To the right of the vertical broken line is shown an interoflice trunk circuit incoming from the manual ofiice to a first group selector or district switch in a mechanical switching otiice. A register sender for controlling the selective switches is also illustrated diagrammatically. F ig; 2 shows the detailed circuits and apparatus of a second group selector or ofiice switch in the mechanical oflice together with a portion of the multiple terminal bank to which the brushes of such switch have access.

The structure and operation of the selective switches disclosed in this application may be the same as shown and described in the patent to Craft and Reynolds No. 1,123,- 696, issued January 5, 1915.

The office selector, shown in detail in Fig. 2, which contains the subject matter of this invention is ofthe well-known multiple rush power-driven type. The terminal bank of the switch in which the multiple terminals of outgoing circuits appear, is usually arranged in five sections. For each section of terminals, a set of brushes is provided on the movable shaft of the switch. These brushes are arranged so as to be normally held out of engagement with the sucs cessive terminal sets in their movement over the surface of the bank. When the switch is taken for use in the extension of a connection, the brush shaft is first advanced under the selective control of the register sender to a position for tripping the set of brushes having access to the desired section of terminals in the bank.

The several sections of terminals in the multiple bank are further subdivided into groups. Each of these groups usually contains a series of terminals of connecting circuits of the same numerical order and of a different numerical order from the terminals of the other groups of the section. In Fig. 2 a portion of two different groups 01 terminals in the same section is shown, the upper group being generally indicated at A and the. lower group being indicated at B. i There is only shown a single set of brushes 227, 228 and 229, this particular set having access to the section of terminals in the back containing the groups A and B. hen the set of brushes having access to the desired set of terminals has been tripped so as to make engagement therewith, the switch is again selectively operated to advance such set of brushes into cooperative relation with the desired group of terminals inthe section. The proper group having been selected, the brush-carrying element is thereupon advanced to move the brushes over the terminals of the selected group in an automatic trunk-hunting movement to search for an idle set of terminals.

Should all the terminals be busy in the group representing trunks or circuits of a given numerical order, the movement of the brushes continues until they have traversed the entire group. In such a case, unless some means is provided to arrest the movement of the switch as soon as the last set of terminals of the group has been tested and foundbusy, the brushes will continue their advance into the next succeeding group which contains terminals representing trunks or circuits of a different numerical order. To prevent the era tension of a false connection on this account, there is usually provided a set of overflow terminals for each of theseveral groups in a section. For example terminals 233, 234, and 235 serve as overflow terminals to the group B, and terminals 237, 233 and 239 serve as overflow terminals to the group A. The electrical condition or" the test terminals of the overflow set is the same as that of all idle test terminals in the group. When, therefore, the brushes reach the overflow terminals, the switch is brought to rest and prevented from falsely entering the succeeding group.

If, however, during the hunting movement of the brushes over the selected group, an idle set of terminals is found, the switch. is stopped in the well-known manner and the electrical condition of the terminals and their multiples in the bank, is immediately altered so as 'to render them busy to other switches. When the brushes advance to the overflow position, it is not desirable that the overflow terminals be rendered busy as is done each time a set of trunk terminals in the group is selected. The reason for this will be obvious. Should the brushes 227, 228 and 229, of the switch shown, find all the trunks in the group B busy and advance to the overflow terminals 233, 234 and 235 and thereupon render these terminals busy, the brushes of some other switch such as brushes 240, 241 and 242, on engaging the multiple terminals 243, 244 and 245 at the overflow position, would not find the proper electrical condition to arrest the movement of the switch. Consequently such switch would continue to advance into the next succeeding group of terminals.

In accordance with this invention the brushes 22'4", 228 and 229 of the switch are brought to rest in response to the electrical condition 01 any set of idle terminals such as 230, 231 and 232 in the group, whereupon the electrical condition of these terminals is immediately altered to render them busy. When the brushes 227, 228 and 229 advance to the overflow terminals 233, 234 and 235, they are likewise arrested in response to the same electrical condition that identifies idle sets of terminals, but in this case the electrical condition of the overflow terminals 1s not changed. Consequently any other selector switch that happens to advance at the same time to the overflow position, will also find the necessary electrical condition on the overflow terminal for stopping the switch, hus preventing the false movement of the switch into the succeeding group of termi- A detailed description of the operation of the switch in the extension of a telephone connection will now be given. The system in which these switches are adapted to operate and the register sender controlling their selective movements, may be in general the same as disclosed in patent to Lundell and Clark No. 1,342,823, issued June 8, 1920. Assume that the subscriber at substation 100, whose line terminates in the manual oflice, desires to extend a telephone connection. The initiation of the call at substation 100 causes the operation of a supervisory signal before the operator in the manual olfice. The operator responds by inserting her answ ring plug 103 in jack 101 of the calling line and ascertains the designation of the called line. The manual operator thereupon converses, by means of an order wire, with the operator in the mechanical otlice whose position is illustrated to the right of the broken line in Fig. 1. The operator in the mechanical ofiice assigns an idle trunk for use and sets up on her keyboard the designation of the called line communicated to her by the distant manual operator. The manual operator thereupon inserts the plug 104 of her cord circuit 102 in jack 105 of th assigned trunk which leads to the mechanical otfice and terminates in the district switch, diagrammatically illustrated by means of the brushes 106, 107 and 108. It is not considered necessary to disclose or describe herein the means by which the called number is communicated over an order wire, the assignment of an idle trunk by the operator in the mechanical office, or the setting of the register sender in response to the actuation of keys on the operators keyboard.

The called line designation having been recorded on the registers of the sender, the district switch is operated under the control of the sender to advance its brushes 106, 107 and 108 into engagement with terminals 109, 110 and 111 of a trunk leading to an idle office selector. The sequence switch 118, which controls the circuits of the district selector in'the usual manner, thereupon advances to a position where the fundamental circuit is closed by way of contacts 112 and 113 to the office selector switch. This circuit may be traced from battery through the right-hand winding of relay 201, lower lefthand contact 263 (1) contact 207 (1 to 4), conductor 264, terminal 109, brush 106, contact 112 of sequence switch 118, conductor 119, winding of stepping relay 116, armature and contact of relay 117, conductor 120,

contact 113 of sequence switch 118, brush 107, terminal 110, conductor 265, contact 209 (1 to 4), to ground. Relays 201 and 116 become energized in this circuit. Relay 201 completes a holding circuit for itself from battery through the right-hand winding and front contact and inner right-hand armature of said relay, outer right-hand armature and contact of said relay, lower righthand contact 263 (1 to 4), to ground at contact 209, as above described. This substitute circuit serves to maintain the energization of relay 201 independent of the lower left-hand contact 263. Relay 201 also completes a circuit from battery through the winding of sequence switch 200, upper right-hand contact 204 (1), front contact and left-hand armature of relay 201 to ground. Sequence switch 200 energizes in this circuit and moves from position 1 into position 2.

In position 2 of sequence switch 200 the up-drive power magnet 211 is energized to cause the upward movement of the brush shaft 246 for determining the tripping of the proper set of brushes. The circuitfor magnet 211 is traceable from battery through the winding of said magnet, lower right-hand and upper right-hand contacts 202 (2), front contact and left-hand armature of relay 201, to ground. As thebrush shaft 246 approaches the first brush tripping position, the brush 221 makes engagement with the first metallic segment of the brush-tripping commutator 213. A circuit is thereupon closed from battery through the right-hand winding and front contact and inner right-hand armature of relay 201, outer right-hand armature and contact of said relay, lower right-hand contact 263 (1 to 4), upper right-hand contact 263 (1% to 2), commutator 213, brush. 221, to ground. This direct circuit to ground at brush 221 maintains relay 201 energized but causes the shunting of the stepping relay 116 in the fundamental circuit. In the well-known manner the deene-rgization of the stepping relay 116 causes the energization and locking up of the first pair of counting relays at the sender. For each succeedingbrushtripping position approached by the brush shaft 246, a pair of counting relays are energized and locked up until the registration at the sender is satisfied, at which time the fundamental circuit is opened as by means of relay 117. Relay 201, however, remains energized after the opening of the fundamental circuit at the sender, so long as the brush 221 is in engagement with a metallic segment of the commutator 213. Yihen' the brush shaft 246 is fully advanced to the corresponding brush-tripping position, the brush 221 engages the next insulating segment of commutator 213 and relay 201 deenergizes. The release of the lefthand armature of relay 201 opens the circuit of the up-drive magnet 211, causing the brush shaft 246 to stop. Relay 201 also completes a circuit from battery through the winding of sequence switch 200, lower left-hand contact 204 (2), back contact and lefthand armature of relay 201 to ground. Sequence switch 200 advances from position 2 into position 3.

)Vith sequence switch 200 in position 3, the fundamental circuit is again closed at contacts 263 and 209 and relays 201 and 116 become energized. Relay 201 completes a circuit from battery through the winding of sequence switch 200, upper right-hand contact 204 (3), front contact and left-hand armature of relay 201 to ground. Sequence switch 200 moves from position 3 into position 4. Relay 201 remains energized in position 4 of sequence switch 200 by means of the substitute circuit closed at contact 263 (1 to 4), as above described. WVith sequence switch 200 in position 4., the up-drive power magnet 211 is energized to cause the advance of the brush shaft 246 in the group-selecting movement. The trip magnet 210 is energized at this time-by means of a circuit from battery through the winding of said magnet, lower left-hand contact 205 to 7), to ground. With the trip magnet 210 energized, the first upward movement of the brush shaft 246 in the group-selecting operation causes the selected set of brushes 227,

and to be tripped so as to make contact with the successive terminals in the groups, sucn as A and B, in the selected section of the terminal bank. As the brush shaft advances the selected set of brushes into cooperative relation with the first group of terminals in the section, the brush 222 makes engagement with the first metallic segment of the group-selecting commutator 215. A circuit is thereby closed from battery through the right-hand winding and front contact and inner right-hand armature of relay 201, outer right-hand armature and contact of said relay, lower righthand contact 263 (1 to 4), upper lefthand contact 263 (3% to 4), commutator 215, brush 222, to ground. This direct circuit to ground serves to maintain the energization of relay 201 and to shunt the stepping relay 110 in the fundamental circuit. For each succeeding group of terminals passed over by the brushes, the stepping relay 116 is similarly shunted. When the desired group of terminals, as for example group B, is reached, the fundamental circuit is opened at the sender. As soon thereafter as the brush 222 engages an insulating portion of the commutator 215, relay 201 releases its armatures and opens the driving circuit of the power magnet 211. Relay 201 also completes a circuit from battery through the winding of sequence switch 200, lower lefthand contact 204 (4), back contact and lefthand armature of relay 201 to ground. Sequence switch 220 moves from position 4 into position 5.

In position 5 of sequence switch 200, relay 201 is immediately energized by means of a circuit from battery through the left-hand winding of said relay, upper left-hand contact 203 (5 to 7), lower right-hand contact 203 (5) to ground. Relay 201 attracts its armatures and completes a circuit from battery through the winding of sequence switch 200, upper right-hand contact 204 (5), front contact and left-hand armature of relay 201 to ground. Sequence switch 200 advances into position 6. If the first trunk in the group B, upon the terminals of which the brushes 227, 228 and 229 are standing at this time, is busy, a ground potential will be present on the test terminal 232 of such trunk. Relay 201, therefore, remains energized in position 6 of sequence switch 200 by means of a circuit from battery through the right-hand winding and front contact and inner right-hand armature of relay 201, outer right-hand armature and contact of said relay, upper left-hand contact 206 (5 to 18), upper right-hand contact 206 to 6%), conductor 247, commutator strip 217, brush 224, test brush 229, to ground at the testterminal 232 of the busy trunk. Relay 201, by remaining energized, completes a circuit from battery through the Winding of the up-drive power magnet 211, lower right-hand and upper right-hand contacts 202 (6), front contact and lefthand armature of relay 201 to ground. Magnet 211 energizes and causes the upwart movement of the brush shaft 246 in the trunk-hunting operation. Relay 201 remains energized to continue the upward movement of the brush so long as test brush 229 encounters the grounded test terminals of busy trunk circuits. Upon reaching the terminals of the first idle trunk, such as terminals 250, 251 and 252, no ground being found on the test terminal 252, relay 201 releases its armatures and opens the circuit of the power magnet 211. The brushes, therefore, come to rest in engagement with the terminals of the idle trunk circuit. Relay 201 also closes a circuit from battery, through the winding of sequence switch 200, lower left-hand contact 204 (6), back contact and left-hand armature of relay 201, to ground. Sequence switch 200 moves out of position 6 and into position 7. Relay 201, by deenergizing, also completes a circuit from ground through its back contact and inner right-hand armature, lower right-hand and lower left-hand contacts 208 (5 to 7), conductor 248, overflow commutator 216, brush 223, test brush-229 to test terminal 252 of the selected trunk. This circuit serves to immediately place a ground on the test terminal 252 to render the multiples of this terminal non-selectable to other switches. As soon as sequence switch 200 reaches position 0%, in passing to position 7, a substitute circuit is closed independent of the armature and contact of relay 201, for applying ground to the test terminal 232. This circuit may be traced from ground, upper right-hand contact 205 (6% to 8%), conductor 248, and thence to the test terminal 232 as above traced.

The overflow commutator designated at 216 comprises a plurality of metallic strips, electrically connected together as shown in the figure. Each of these strips is individual to a group of terminals such as groups A and B in the section. These strips are of such length and so disposed with respect to the cooperating brush 223 that said brush is in engagement with a given strip during the time that the brushes 227, 228 and 229 are making contact with any of the sets of trunk terminals in the corresponding group. Hence the above-traced circuit for applying ground to the test terminals of any selected trunk in the group is closed through the corresponding strip of the overflow commutator 216. If, however, the brushes 227, 228 and 229 move over the entire group of trunk terminals and engage the overflow terminals 233, 234 and 235, the brush 223 passes off the corresponding strip of the overflow commutator 216 and rests between two adjacent strips of such commutator.

With sequence switch 200 in position 7 and relay 201 deenergized, a circuit is closed from battery through the left-hand winding of said relay, upper left-hand contact 203 (5 to 7), lower right-hand contact 203 (7), to ground. Relay 201 attracts its armatures and locks up in a circuit as follows: battery, through the right-hand winding and front contact and inner right-hand armature of relay 201, outer right-hand armature and contact of relay 201, upper right-hand contact 206 (5 to 18), low-er left-hand contact 206 (7 to 18), conductor 249, terminal 111, brush 108, to ground at the close-d contact 114 of sequence switch 118. Relay 201 also completes a circuit from battery through the winding of sequence switch 200, upper right-hand contact 204 (7), front contact and left-hand armature of relay 201, to ground. Sequence switch 200 thereupon passes into position 8 which is the talking position. With sequence switch 200 in position 8, the fundamental circuit is closed by way of contacts 207 and 208, conducting strips 219 and 218, brushes 226 and 225, brushes 227 and 228, terminals 250 and 251, and trunk conductors 253 and 254 for controlling the necessary number of succeeding selective switches to complete the extension of the connection.

Then the conversation is over a supervisory signal (not shown) is operated in any well-known manner, to advise the operator in the manual oflice that the connection is no longer desired. Shethereupon removes plugs 103 and 104 from the corresponding jackslOl and 105. The removal of plug 104 from jack 105 serves to display a disconnect signal (not shown) before the operator in the mechanical exchange. This latter operator then depresses the usual disconnect key to cause the release of the dis trict selector. The restoration of the district selector opens, at contact 114 andtest brush 108, the holding circuit of relay 201 at the oflice selector. Relay 201 deenergizes and closes a circuit from battery through the winding of sequence switch 200 to lower left-hand contact 204 (8 to 17), back contact and left-hand armature of relay 201, to ground. Sequence switch 200 advances from position 8 into position 18. In this position a circuit is established from battery through the winding of the down-drive power magnet 212, lower left-hand contact 203 (18) lower right-hand contact 203 (18). to ground. Power magnet 212 energizes and causes the restoration to normal of the brush shaft 246. In the normal position of the brush shaft a circuit is closed from battery through the winding of sequence switch 200, upper left-hand contact 204 (3 to 18),

segment 255, brush 222, to ground. Sequence switch 200 moves from position 18 into position 1. The apparatus is now fully restored to its normal condition.

It will next be assumed that duringthe trunk-hunting operation of the selected set of brushes 227, 228 and 229, all trunks in the group B are busy. In this case the brushes traverse the entire group of trunk terminals and finally engage the overflow terminals 233, 234 and 235, located between the adjacent groups A and B. No ground potential being present on the test terminal 235 of the overflow set, relay 201 releases its armatures and completes the circuit hereinbefore traced for moving sequence switch 200 out of position 6 and into position 7. The circuit traced for the application of ground to the test terminals of trunk circuits including the back contact and inner righthand armature of relay 201, sequence switch contact 208, conductor 248 and overflow commutator 216, is now open since the brush 223 is resting between two adjacent metallic strips of said commutator. Therefore, the retraction of the armature of relay 201 at the end of the trunk-hunting movement, does not cause the application of ground potential to test brush 229 and in turn to the test terminal 235 and its multiples at the overflow position. Likewise the closure of the upper right-hand contact 205 which takes place immediately following the release of relay 201, is without effect to alter the electrical condition of the test brush 229 and test terminal 235 of the overflow set. This being true, the brushes 240. 241 and 242 of some other switch, which may be in engagement at this time with the multiple terminals 243, 244 and 245, at the overflow position, will find no ground potential on the test terminal 245 to cause the improper advance of such switch into the adjacent group of trunk terminals. A notification may be given to the operators of the busy condition of the trunk group and the partially established connection may be released in any suitable manner, such as described in the patent to Lundell and Clark, No. 1,342,823, issued June 8, 1920.

In some cases where it is desirable to enlarge the trunk groups of a particularnumerical order, that is trunk groups leading to certain switching stages in the system, it is necessary to assign two or more groups of terminals A and B for this purpose. In such an arrangement it is necessary to provide some means whereby the brushes, after having found all trunks in the first group busy, may continue to advance in their trunkhunting movement into the succeeding groups of trunks. To accomplish this the multiple test terminals 235 and 239 of the overflow sets may be connected directly to ground as by means of keys 256 and 257.

What is claimed is:

1. In a selective switch, a series of sta tionary terminals, a movable element arranged to cooperate with said terminals, means for driving said movable element, selective means responsive to the electrical condition of certain oi said terminals for stopping said movable element to select any one thereof, a circuit including said movable element, means for closing said circuit to change the electrical condition of said mo able element to in turn change the electrical condition of the selected terminal, said selective means being responsive to the electrical condition of a particular terminal of said series for stopping the movable element to select such terminal, and means for opening said circuit when said particular terminal is selected to prevent the changing of the electrical condition of the movable element.

2. In a selective switch, a series of staionary terminals, a movable element arranged to cooperate with said terminals, means for driving said movable element, selective means responsive to the electrical condition of certain of said terminals for stopping the movable element to select any one of such terminals, a circuit including said movable element, means operated each time the movable element is stopped for closmg said circuit at one point to change the electrical condition of the movable element to in turn change the electrical condition of the selected terminal, said selective means being responsive to the electrical condition of a particular terminal of said series for stopping the movable element to select such terminal, and means for opening said circuit at another point when the particular terminal is selected to prevent the changing of the electrical condition of the movable element.

3. In a selective switch, a series of stationary terminals, a movable brush arranged to engage said terminals, selective means responsive to a ground potential on certain of said terminals for controlling the movement of said brush, said means responding to the absence of ground potential on any terminal for stopping the brush to select such terminal, a circuit including said brush, means for closing said circuit to apply a ground potential to said brush to in turn apply a ground potential to the selected terminal, said selective means responding to the absence of ground potential on a particular terminal in said series for stopping said brush to select such terminal, and means for opening said circuit when said particular terminal is selected to prevent the application of ground potential to said brush.

4. In a selective switch, a series of'stationary circuit terminals, an overflow terminal at the end of said series, a movable brush arranged to successively engage all of said terminals, means for driving said brush, selective means responsive to the electrical condition of said circuit terminals for stopping said brush to select any one thereof, a circuit including said brush, means for clos ing said circuit to change the electrical condition of said brush to in turn change the electrical condition of the selected circuit terminal, said Selective means being re sponsive to the electrical condition of said overflow terminal for stopping the movable brush to select said overflow terminal, and means for opening said circuit when the overflow terminal is selected to prevent the changing oi? the electrical condition of said brush.

5. In a selective switch, a plurality of series oi stationary terminals, a movable brush arranged to cooperate with said terminals, means for driving said brush to select any one of said series and for driving said brush over the terminals of such series, selective means responsive to the electrical condition of certain of the terminals in the series for stopping said movable brush to select any one thereof, a circuit including said movable brush, means for closing said circuit to change the electrical condition of said movable brush to in turn change the electrical condition of the selected terminal, said selective means being responsive to the electrical condition of a particular terminal in the selected series for stopping the movable brush to select such terminal, and means for opening said circuit when said particular terminal is selected to prevent the changing of the electrical condition of the movable brush.

6. In a selective switch, a series of stationary terminals, a movable brush'arranged to cooperate with said terminals, means for driving said brush, a test relay responsive to the electrical conditionof certain of said terminals for stopping said movable brush to select any one thereof, a circuit including said movable brush, said circuit being closed by said test relay to change the electrical condition of the movable brush and in turn change the electrical condition of the selected terminal, said test relay being responsive to the electrical condition of a particular terminal of said series for stopping the movable brush to select such particular terminal, and means for opening said circuit when said particular terminal is selected to prevent the changing of the electrical condition of the movable brush.

7. In a selective switch, a plurality of sets of stationary terminals, trunk conductors connected therewith, other sets of stationary terminals to which no trunk conductors are connected, a movable terminal for selecting said stationary terminals and means arranged to alter the electrical condition of the movable terminal when it selects a set of terminals to which trunk conductors are connected and to leave its electrical condition unaltered when it selects a set of terminals to which no trunk conductors are connected.

8. In a selective switch, a plurality of sets of stationary terminals, trunk conductors connected therewith, other sets of stationary terminals to which no trunk conductors are connected, a brush movable over said terminals to select any one set of said terminals and means when said brush selects stationary terminals to which trunk conductors are connected for altering the electrical condition of the brush to in turn alter the electrical condition of the associated selected terminal and for leaving the electrical condition of said brush unaltered when it selects a set of stationary terminals to which no trunk conductors are connected.

9. In a selective switch, a plurality of sets of terminals, trunk conductors connected therewith, other sets of terminals to which no trunk conductors are connected, a movable element, means for advancing said element to select and engage any one of said sets of terminals and means for changing the electrical condition of said element when it selects terminals to which trunk conductors are connected and leaving its electrical condition unchanged when it selects others of said terminals to which no trunk conductors are connected.

10. In a selective switching system, a plurality of multipled stationary terminals, a plurality of selective switches each having a movable terminal for selecting said stationary terminals, means arranged to alter the electrical condition of the movable terminals of said switches when individually selecting certain of the stationary terminals and leaving the electrical condition unaltered when a plurality of said switches simultaneously select a certain one of said multipled stationary terminals.

In Witness whereof, we hereunto subscribe our names this 27th day of December, A. D.

FRANK N. REEVES. EDGAR H. CLARK. 

